All right. Ocean temperatures, from Alaska down here to California, have been rising. This is a marine heat wave, and scientists say it looks a lot like a mass of warm water that appeared five years ago and was nicknamed "the blob." Cassandra Profita with Oregon Public Broadcasting has more.

CASSANDRA PROFITA, BYLINE: The current marine heat wave isn't quite as big or as warm as the blob, at least, not yet. But the last heat wave caused major upheaval in the ocean. A toxic algae bloom made it unsafe for people to eat shellfish up and down the coast so many crab and clam fisheries were closed. Salmon and sea lions had less food to eat, and warm-water species started showing up farther north. Chris Harvey is a biologist with the National Marine Fisheries Service.

CHRIS HARVEY: Given the severity of the last marine heat wave, the blob, we definitely felt it was our responsibility at this point to say this is something that we are concerned about, and we're going to continue watching it with regular monitoring along the West Coast.

PROFITA: Harvey says one of the unexpected consequences of the blob was that more whales got entangled in fishing gear while searching for food closer to shore.

HARVEY: We didn't anticipate that at all. We should expect there to be some surprises that we currently can't anticipate if this event persists for years, like that last one did, and if it's extent and magnitude remains as severe.

PROFITA: Scientists say it's possible a change in the weather could end the heat wave. Nate Mantua with the Southwest Fisheries Science Center says the warm water is the result of an unusual weather pattern that's caused winds to be weaker than normal for months. That means cold water at the bottom of the ocean is not moving up toward the top. Scientists don't know if that's connected to the human-caused climate change that's warming the planet.

NATE MANTUA: We don't know if the weather pattern is. We do know that there's an underlying warming that has boosted ocean temperatures every year.

PROFITA: Right now, water temperatures are about 5 degrees above normal off the western U.S. Scientists expect the heat wave to hurt salmon populations and the fisheries that depend on them. It could also cause a shift in marine species to cooler waters. For NPR News, I'm Cassandra Profita in Portland. Transcript provided by NPR, Copyright NPR.